Bruker BioSpin Solid State NMR, User Manual

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User Manual Version 002 BRUKER BIOSPIN 291 (327)
24
CRAMPS 2D 24
CRAMPS methods allow measurement of chemical shifts in the presence of
strong homonuclear dipolar interactions. Therefore, CRAMPS-type sequences
can be applied to measure chemical shifts of protons (where these sequences
work most efficiently, and where fast spinning cannot easily be used). As an ex-
ample, the proton-X heteronuclear chemical shift correlation experiment (see
chapter 5) uses FSLG to suppress homonuclear dipolar couplings between pro-
tons to resolve the proton chemical shifts. CRAMPS-type pulse sequences must
be used in both dimensions if proton chemical shifts are to be correlated.
Two types of proton-proton correlation experiment will be described here:
1. Proton-proton shift correlation via spin diffusion (similar to the high resolution
NOESY-experiment). In this case, the dipolar coupling between protons acts
during the mixing period. The size of the off-diagonal cross peaks indicates the
size of the dipolar coupling between the correlated sites.
2. Proton-proton DQ-SQ correlation (similar to the high resolution INADEQUATE)
correlates proton chemical shifts with DQ-frequencies of dipolar coupled sites.
The modifications according to the chapter
"Modified W-PMLG"
are implement-
ed in order to remove the carrier spike. Without a carrier spike, 2D experiments
are much easier and faster to set up. Being able to set the carrier close to the de-
sired spectral range, one can make the total acquired window smaller as well
along F2 (using digital mode) as along F1.
References:
1. P. Caravetti, P. Neuenschwander, R.R. Ernst, Macromolecules, 18 , 119 (1985).
2. S.P. Brown, A. Lesage, B. Elena and L. Emsley , Probing Proton-Proton Proximities in the Solid State:
High-Resolution Two-Dimensional
1
H-
1
H Double-Quantum CRAMPS NMR Spectroscopy, J. Am.
Chem. Soc. 126 , 13230 (2004).
Proton-Proton Shift Correlation (spin diffusion) 24.1
The standard CRAMPS setup must be executed first (see chapter
22
,
23
). Any
homonuclear dipolar decoupling scheme may be used, but in the following the ex-
periment is described using windowed pmlg (w-PMLG). The reasons are the fol-
lowing:
1. At fast spin rates over 10 kHz, only w-PMLG and DUMBO work well. The se-
quence can easily be modified to use DUMBO, replacing the w-PMLG shapes
by DUMBO-shapes and modifying the shape timing accordingly.
2. W-PMLG is easy to set up, since it is rather insensitive to power level missets
and frequency offsets. When the experiment setup for the 1D experiment has
been executed, no further setup is required for the 2D experiment. Start from
the 1D experiment on your sample (the recommended setup sample is gly-
cine) and generate a 2D data set by clicking on the symbol 1, 2 in the headline
of the acquisition parameters.